Atoms, Electrons and Electric Charge
Every component in your radio — from the front-end filter to the final amplifier transistor — works by controlling the movement of electrons through matter. To understand electronics at any level beyond button-pushing, you need to know what electrons are, where they come from and why some materials release them freely while others hold them tight. This lesson starts at the very beginning: the atom.
What Is an Atom?
Think of an atom like a tiny solar system. At the center is the nucleus, which plays the role of the sun. The nucleus is made up of two types of particle: protons, which carry a positive electric charge, and neutrons, which carry no charge at all. Orbiting the nucleus at various distances — like planets orbiting the sun — are electrons, each carrying a negative electric charge.
The number of protons in the nucleus is called the atomic number and defines which element the atom is. Hydrogen has 1 proton, copper has 29, iron has 26. In a neutral atom, the number of electrons exactly equals the number of protons. Because the positive charges of the protons are balanced by the negative charges of the electrons, the atom as a whole is electrically neutral — it has no net charge.
Electrons do not all orbit at the same distance. They are arranged in shells (also called energy levels), with each shell able to hold a fixed maximum number of electrons. The innermost shell holds up to 2 electrons, the next holds up to 8, and so on. The outermost shell — called the valence shell — is the most important one for understanding electrical conduction.
A simplified atom showing the nucleus (protons and neutrons) at the center with electrons orbiting in shells. The outermost electron in a metal atom is loosely held and can break free.
View LargerElectric Charge
Electric charge is a fundamental property of matter, just like mass. Protons carry a positive charge and electrons carry a negative charge. The basic rule of charge is simple: like charges repel, unlike charges attract. This is the same force that keeps electrons in orbit around the nucleus — the attraction between the negative electrons and the positive protons holds the atom together.
The unit of electric charge is the coulomb (C), named after French physicist Charles-Augustin de Coulomb. One electron carries an incredibly tiny charge of 1.6 × 10−19 coulombs. To put that in perspective, it takes 6.24 × 1018 electrons flowing past a point every second to produce a current of just 1 ampere. That is over six billion billion electrons per second — yet a standard 13.8V ham supply can deliver 20 A, meaning 1.25 × 1020 electrons per second are on the move through the wire.
When an atom gains or loses electrons, it is no longer neutral. An atom with extra electrons has a net negative charge and is called a negative ion (anion). An atom that has lost electrons has a net positive charge and is called a positive ion (cation). Ion formation is important in battery chemistry and in the behavior of electrolytic capacitors.
Conductors, Insulators and Semiconductors
The key to whether a material conducts electricity lies in its valence shell — the outermost electron shell. If the valence shell is nearly empty and the outer electron is weakly held, that electron can break free of its parent atom and wander through the material. These wandering electrons are called free electrons or conduction electrons.
Conductors (metals such as copper, aluminum and silver) have one or two loosely held electrons in their valence shells. At room temperature, ordinary thermal energy is enough to shake these electrons free. A cubic metre of copper contains approximately 8.5 × 1028 free electrons — an enormous reservoir of mobile charge. In the absence of an applied voltage, these free electrons move randomly in all directions and produce no net current. Apply a voltage across the copper and they all acquire a slight drift in one direction: that drift is electric current.
Insulators (rubber, glass, PVC plastic, air) have full or nearly full valence shells. Their outer electrons are tightly bound and require very large amounts of energy to break free. At normal operating voltages, essentially no free electrons exist in an insulator and negligible current flows. This is why plastic-coated wire does not shock you and why PCB material can sit between copper tracks at different voltages without conducting between them.
Left: in a conductor, free electrons drift through the lattice of metal atoms. Right: in an insulator, electrons are tightly bound to their parent atoms and cannot move freely.
View LargerSemiconductors (silicon, germanium, gallium arsenide) sit between conductors and insulators. Pure silicon at room temperature has very few free electrons — not enough to conduct well, but not zero either. What makes semiconductors extraordinary is that their conductivity can be precisely controlled. By adding tiny quantities of impurity atoms — a process called doping — engineers create regions with an excess of free electrons (n-type silicon) or a deficit of electrons, which behaves like an excess of positive charges called holes (p-type silicon). The junction between n-type and p-type material forms a diode. Two junctions back to back form a transistor. Everything in modern electronics — the ICs in your radio, the DSP chip, the microcontroller — is built from carefully arranged semiconductor junctions.
Electron Flow and Conventional Current
When you connect a battery to a piece of wire, the battery's chemistry creates a surplus of electrons at its negative terminal and a deficit at its positive terminal. The free electrons in the wire are repelled from the negative terminal and attracted toward the positive terminal. Electrons therefore flow from the negative terminal, through the external circuit, to the positive terminal. This is called electron flow or electron current.
However, when scientists first studied electricity in the 18th century — more than a century before electrons were discovered — they assumed that some positive substance flowed from the positive terminal to the negative. This assumption was built into every formula, law and circuit diagram developed in that era. When J.J. Thomson discovered the electron in 1897 and its direction of flow was determined, it turned out to be opposite to the assumed direction. By then, the convention was too deeply embedded to change.
The result is that we have two valid but opposite conventions:
- Conventional current flows from positive (+) to negative (−) through the external circuit. This is used in all circuit diagrams, Ohm's Law, Kirchhoff's Laws and power calculations.
- Electron flow (actual physical flow) goes from negative (−) to positive (+). This is relevant when the physical direction matters — for example, when understanding how a diode or transistor works at the carrier level.
For all practical circuit analysis in this course, conventional current is used throughout. The direction only becomes critical when you move into semiconductor physics.
When voltage is applied across a conductor, free electrons drift from the negative terminal toward the positive terminal. Conventional current is defined as flowing in the opposite direction.
View LargerWhy This Matters for Ham Radio
Your antenna is simply a piece of wire or aluminum tubing. When a radio wave from a distant transmitter arrives at your antenna, the oscillating electric field of that wave exerts a force on the free electrons in the metal. The electrons oscillate back and forth in response, producing a tiny alternating current. That current travels down the feedline to your receiver's front end, where it is amplified and processed. The received signal is, at its most fundamental level, the wiggling of electrons.
Transmitting works in reverse. Your transmitter drives a large, carefully shaped oscillating current through the antenna. Accelerating electrons radiate electromagnetic energy — that is the radio wave you are launching into space. The efficiency of that process depends on the antenna's physical length relative to the wavelength of the signal, on the conductivity of the metal and on the impedance of the feedline — all concepts that trace back to the behavior of electrons in conductors.
Every stage of your radio — low-noise amplifier, mixer, IF filter, demodulator, power amplifier — is a circuit that controls and shapes the movement of electrons through conductors and semiconductors. Knowing what electrons are, where they come from and why they move when voltage is applied is therefore the true foundation of radio electronics. Every topic in this course builds on the concepts introduced in this lesson.
Frequently Asked Questions
What is a free electron and why do metals have them?
A free electron is an electron that has broken away from its parent atom and is free to move through the material. Metals have a particular atomic structure where the outermost electron is only weakly bound to the nucleus. At room temperature, thermal energy is enough to shake these electrons loose. A piece of copper contains approximately one free electron per atom — around 8.5 × 1028 free electrons per cubic metre. This vast reservoir of mobile charge carriers is why metals are such good conductors.
Why does conventional current flow in the opposite direction to electrons?
When scientists first studied electricity in the 18th century, they had no way to see individual electrons — those were not discovered until 1897. Early researchers assumed that positive charge was the thing that flowed, moving from the positive terminal of a battery to the negative. When electrons were eventually discovered, it turned out they moved the other way. By then, every circuit diagram, formula and textbook used conventional current. Rather than rewrite everything, the scientific community kept the convention. For nearly all practical purposes (Ohm's Law, Kirchhoff's Laws, power calculations), conventional current gives correct results — the direction you use only matters when the actual physical direction of charge flow is important.
What is a semiconductor and why is it important?
A semiconductor such as silicon or germanium sits between conductors and insulators in terms of electrical conductivity. Pure silicon has very few free electrons at room temperature. By adding small amounts of impurities (a process called doping), it is possible to create regions with an excess of electrons (n-type) or a shortage (p-type). The junction between n-type and p-type silicon forms a diode. Two junctions back to back form a transistor. All modern electronics — radio ICs, microprocessors, power control circuits — are built from semiconductor junctions.
Is current carried by electrons or by something called holes?
In metals, current is carried entirely by free electrons. In semiconductors, both electrons and holes carry current. A hole is simply the absence of an electron in a covalent bond — it behaves like a positive charge moving in the opposite direction to electron flow. In p-type semiconductor material, holes are the majority charge carrier. In circuit analysis you do not need to track holes and electrons separately — conventional current covers both cases.
Test Your Knowledge
Answer the questions below to check your understanding. Every answer can be found in the lesson above.